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You may have misunderstood! array_diff_assoc() Several common pitfalls and misunderstandings in official documents
array_diff_assoc() is a very practical function in PHP. It is used to compare key-value pairs of two arrays and return a different part of the first array than the second array. Although this function is very intuitive, developers tend to misunderstand its behavior during use. Today, we will explore several common pitfalls and misunderstandings in array_diff_assoc() to help you better understand how it works.
array_diff_assoc() not only compares the values in the array, but also compares the keys in the array. Therefore, two arrays are considered "different" even if the values are the same, as long as the keys are different. This is different from the behavior of the array_diff() function, which only compares values and does not care about keys.
$array1 = [
0 => 'apple',
1 => 'banana'
];
$array2 = [
1 => 'banana',
0 => 'apple'
];
$result = array_diff_assoc($array1, $array2);
print_r($result);
Output:
Array
(
[0] => apple
)
explain:
Although the values in $array1 and $array2 are the same, array_diff_assoc() thinks they are different because of their different keys.
array_diff_assoc() strictly compares the values and keys of the array, which means it not only checks the types, but also checks whether the types of the values match. That is, the number 1 and the string '1' will be considered different.
$array1 = [
'a' => 1,
'b' => '2'
];
$array2 = [
'a' => '1',
'b' => 2
];
$result = array_diff_assoc($array1, $array2);
print_r($result);
Output:
Array
(
[a] => 1
[b] => '2'
)
explain:
array_diff_assoc() treats the number 1 and the string '1' as different values. Similarly, '2' and 2 are also considered different. This strict comparison will make us pay more attention to the type of data and avoid unexpected results.
If the first parameter of array_diff_assoc() is an empty array, it will directly return the empty array. This behavior is reasonable, but some developers may misunderstand that an empty array will return to the original array. In fact, array_diff_assoc() returns non-empty differential results only if both arrays have content and there are differences.
$array1 = [];
$array2 = [1 => 'apple', 2 => 'banana'];
$result = array_diff_assoc($array1, $array2);
print_r($result);
Output:
Array
()
explain:
Since $array1 is empty, array_diff_assoc() returns an empty array indicating that there is no difference. This may lead some developers to mistakenly think that there is something wrong with the function.
array_diff_assoc() only compares key-value pairs of one-dimensional arrays. If an array contains nested arrays, array_diff_assoc() does not recursively compare key-value pairs of these nested arrays.
$array1 = [
'a' => ['apple', 'orange'],
'b' => 'banana'
];
$array2 = [
'a' => ['apple', 'orange'],
'b' => 'banana'
];
$result = array_diff_assoc($array1, $array2);
print_r($result);
Output:
Array
()
explain:
Even if the values in array1 and array2 contain nested arrays, array_diff_assoc() will still consider these two arrays equal because it does not recursively compare the contents of the nested array. If you need to compare nested arrays, you may need to use other methods or recursive functions.
The array returned by array_diff_assoc() contains only key-value pairs that are different from the first array. If there is no difference, the function returns an empty array. Many developers ignore this when using it, causing them to misunderstand the return results.
$array1 = [1, 2, 3];
$array2 = [1, 2];
$result = array_diff_assoc($array1, $array2);
print_r($result);
Output:
Array
(
[2] => 3
)
explain:
In this example, array_diff_assoc() returns an array element with a key of 2 and a value of 3 , indicating that it exists in $array1 and does not exist in $array2 .
